Connecting to Telstra T-voice 503

I'm helping to set up internet connection to my parents house which they never have internet before. When the NBN was available in their area, A Telstra technician went to their house and change all the phones to DECT phones, they are connected wirelessly to Telstra Gateway.

Obviously the TP-Link NBN hub that I received from tpg can not be connected with this DECT phone wirelessly. So I'm thinking to connect the Telstra Gateway to the TP-Link in a way that I can use those phones.

Hi @Jcwyeung It appears that the Telstra T-voice 503 is only compatible with Telstra gateways, you may have to look at buying a separate DECT system such as a Panasonic or Uniden with 1 - 3 handset units and simply plug the base into the phone 1 port on TPG supplied modem/router.